Wireless Local Area Network (WLAN) has undergone vast development in order to increase throughput. Task groups such as 802.11b, 802.11a, 802.11g and 802.11n have demonstrated continuous improvement of the WLAN radio throughput. 802.11ac is another task group that is developing the WLAN radios that operate at a frequency spectrum below 6 GHz and especially at 5 GHz. There exist other task groups within the IEEE 802.11 standardization.
Channelization rules for 802.11ac radios are currently under development. The rules define the frequency channels available for 802.11 ac transmitters. The rules are based on a scheme of a primary channel and secondary channels. The scheme follows a principle where each network or basic service set (BSS) has a primary channel and zero or more secondary channels. The primary channel is used for channel contention, and transmission opportunity (TXOP) is gained based on carrier sensing on the primary channel. A BSS allocates its secondary channel preferably to a frequency band not occupied by a primary channel of another BSS. Furthermore, the contending station (STA) may use the secondary channel for transmission only if the secondary channel has been free for a given time prior to a TXOP start time.